Mysql 如何使用SQL中的其他表计算每一行？

我有两张桌子：书桌和作者桌。我需要计算每个作者在图书表中注册的图书数量。怎么做

SELECT *,
       (SELECT Count(dbo.Book.ID)
        FROM   dbo.Book
        WHERE  dbo.Book.AuthorID = dbo.Author.ID) AS NumberOfBooks
FROM   dbo.Author 

---

您必须用一个ID连接两个表，以便找出两个表之间的关系。

sql语句中有一个名为count的group函数，您可以在其中添加group 比如说

SELECT author_name
       Count(books.id)
FROM   author,
       book
WHERE  book.author_id = author_id 
GROUP BY AUTHOR

---

我想这会对你有所帮助。我已经练习过了。你的问题是SQLFIDDLE

以下是我使用的SQL模式：

create table book(  
  book_id int,
  author_name varchar(100),
  book_name varchar(100)
);
create table author(  
 author_id int,
 author_name varchar(100)
);
insert into author values(1, 'shovon');
insert into author values(11, 'arsho');
insert into author values(111, 'soda');
insert into author values(1111, 'nfs');
insert into book values(1, 'shovon', 'book shovon 1');
insert into book values(2, 'soda', 'book soda 1');
insert into book values(3, 'shovon', 'book shovon 2');
insert into book values(4, 'arsho', 'book arsho 1');
insert into book values(5, 'ar', 'book ar 1');

select a.author_name, count(b.book_name) from 
(author as a 
  left join book as b on 
  a.author_name=b.author_name) 
group by a.author_name
order by count(b.book_name) desc;

以下是我使用的查询：

create table book(  
  book_id int,
  author_name varchar(100),
  book_name varchar(100)
);
create table author(  
 author_id int,
 author_name varchar(100)
);
insert into author values(1, 'shovon');
insert into author values(11, 'arsho');
insert into author values(111, 'soda');
insert into author values(1111, 'nfs');
insert into book values(1, 'shovon', 'book shovon 1');
insert into book values(2, 'soda', 'book soda 1');
insert into book values(3, 'shovon', 'book shovon 2');
insert into book values(4, 'arsho', 'book arsho 1');
insert into book values(5, 'ar', 'book ar 1');

select a.author_name, count(b.book_name) from 
(author as a 
  left join book as b on 
  a.author_name=b.author_name) 
group by a.author_name
order by count(b.book_name) desc;

---

SQLFIDDLE的Url

为我们提供您的表的方案选择author，count*from book group by author您确定您只有2个表吗？如果一本书有多个作者会怎样？顺便说一句，熟悉分组和计数。你至少应该自己试试，告诉我们你哪里有问题。一段带有表的模式的代码也很好，这是过于复杂和低效的。此外，这遵循ms sql语法，而不是mysql。那么您有什么建议？您能提出更有效的方法吗？如果您使用视图进行这种类型的报告，效果会更好。@m0riartis我已经在一篇评论中告诉过您：使用group by和count.EDIT选择Countdbo.Book.ID，dbo.Book内部的dbo.AUTHER.Name加入dbo.Book上的dbo.AuthorID=dbo.AUTHER.ID group by dbo.AUTHER.Name这将返回单个作者的结果，不是所有的。